1. Field of the Invention
This invention relates to the manufacture of vital wheat gluten with substantially no objectionable flavor or aroma and thus suitable for use in various food products, which may also contain meat, poultry or dairy analogues.
2. Description of the Related Art
Vital wheat gluten, often simply called wheat gluten, is a vegetable protein product extracted by aqueous processes from wheat or wheat flour. Various gluten extraction processes are described for example in U.S. Pat. Nos. 2,797,212 (Miley et al.), 3,463,770 (Fellers), 3,493,384 (Fellers), 3,498,965 (Fellers), 3,501,451 (Fellers), 3,574,180 (Johnston et al.), 4,486,342 (Bateson et al.) and 4,494,530 (Jansma et al.). The contents of these patents are hereby incorporated herein by reference.
Commercially available vital wheat gluten has the following typical composition (by weight):
______________________________________ Moisture 5 to 8% Protein, % N*5.7, dry basis 75 to 81% Free Lipids, dry basis 0.3 to 2.5% Total lipids, by acid hydrolysis 5 to 9% Ash, dry basis 0.5 to 1.5% ______________________________________
The bread-baking properties of wheat flour are mainly due to the unique visco-elastic properties of its gluten protein. In order to preserve these properties, the processing conditions, especially temperature, are critical.
Vital wheat gluten can be spray dried as in U.S. Pat. No. 2,891,045 (Montgomery et al.), or drum dried as in U.S. Pat. No. 2,567,980 (Tuomy et al.), but most commercially produced vital wheat glutens are flash dried, for example in a process such as that described in U.S. Pat. No. 2,559,551 (Weber). The contents of these patents are hereby incorporated herein by reference.
Flash drying produces a dry powdered gluten suitable for typical gluten uses such as in bread-baking where the gluten is added to strengthen low protein flours or flour doughs which contain added fibre, protein, grains or other product which dilute and weaken the functional native wheat flour protein. Gluten is also used in the preparation of restructured pet food products, such as described in Canadian patent 910115.
Vital wheat gluten is also formulated into pasta and breakfast cereals to improve their nutritional profile, and is added to shrimp feed formulations not only as a source of high quality protein but also in order to impart water stability properties to the feed products.
The heat setting properties of vital wheat gluten are also utilized in the preparation of meat analogues and in the extension of meat, poultry, dairy and surimi based products.
Freshly extracted wet gum gluten has a solids content of from about 30 to about 40%. It is then normally dried in a ring drier, which is a flash dryer of the kind as described for example in U.S. Pat. No. 2,559,551 (Weber) mentioned above. The ring drying process involves extruding wet gum gluten through a disintegrator into a recycling current of dry gluten and hot air. The recycling gluten prevents reagglomeration and promotes disintegration.
Unfortunately, the conditions in this known drying process are also conducive to the initiation of rancidity, since drying temperatures up to about 155.degree. C. are used. Vital wheat gluten contains a certain proportion of lipids, typically from about 5 to about 9% on a dry basis, and these will oxidize readily at such high temperatures, especially in the presence of oxygen. The commercially available gluten currently being ring dried consequently has a rancid "wheaty" or "cereal" flavor and aroma.
Thus, the cereal flavor and aroma of such wheat gluten limits its addition or substitution level and often requires some reformulation in order to mask the foreign "wheaty" or "cereal" flavor.
Other vegetable protein products also have off-flavors. For example, U.S. Pat. No. 4,265,925 (Campbell et al.) describes a solvent process to improve the flavor (referred to as being "beany" or "painty") of soy protein products. Campbell et al. propose an aqueous alcohol solution to extract the flavor and the soluble carbohydrate components of defatted vegetable protein flakes.
U.S. Pat. No. 4,075,361 (Oberg) teaches hot alkaline water extraction of whole soybean in order to deactivate the lipoxygenase enzyme responsible for the "painty" soy flavor.
U.S. Pat. No. 4,108,847 (Creinin) describes a process for preparing a bland corn gluten product. This process would not be suitable for the preparation of a bland vital wheat gluten product since in a critical step the protein slurry is heated to about 90.degree.-100.degree. C. This heating step would denature vital wheat gluten proteins, making it unsuitable for many important traditional uses, for example the manufacture of a wheat gluten based fibrous meat-like product, such as described in U.S. Pat. No. 4,938,976 (Shemer), or the fabrication of a simulated meat pet food product such as described in Canadian patent 910115.
U.S. Pat. No. 4,396,637 ((Singer) teaches a method for processing and drying a vital wheat gluten having improved flavor and odor but without any denaturation of the protein. The vital wheat gluten extracted from wheat or wheat flour in a conventional manner is dispersed in a hydrophobic phase and dried under reduced pressure. However, considerable capital expenditure would be required to substitute such a drying process for the conventional flash drying process. Also, the resulting product would differ from conventional vital wheat gluten in that its composition would be changed from having about 15% to having about 50% carrier oil. Removing this oil component would require additional expensive steps, such as solvent extraction and steam stripping.
U.S. Pat. No. 4,645,831 (Lawhon) describes a process for improving the flavor and the color of wheat gluten products. The gluten or gluten products are dispersed in an alkaline water solvent phase and then extracted. The extracted protein concentrate is re-dispersed in a suitable solvent and further purified by ultra-filtration. This process would add a series of additional complex steps to the process of starch and gluten separation, namely the dispersion in an alkaline aqueous solvent phase, the recovery of the solvent and the ultra-filtration. Also, the extra equipment needed for the ultra-filtration and the solvent recovery systems would require large capital expenditures.
Thus, although there has been a need for vital wheat gluten with substantially no objectionable flavor or aroma for many years, and various attempts have been made to provide a suitable process for producing such gluten, the only processes so far proposed require the addition or substitution of expensive steps in conventional gluten producing processes.
There is therefore still and has for a long time been a need for a simple and inexpensive modification to conventional gluten producing processes which include drying wet gum gluten to enable dried vital wheat gluten to be produced with substantially no objectionable flavor or aroma.